Comprehensive characterization of hemicelluloses obtained from Gleditsia sinensis Lam. pods and the application of moderately degraded hemicelluloses in galactomannan film.

The Gleditsia sinensis Lam. pods (GSP) are consistently discarded as waste after saponin extraction due to a lack of industrial or high-value utilization. Herein, the hemicelluloses were extracted from two varieties of GSP and subjected to comprehensive characterization. The molar mass of DMSO-soluble hemicelluloses (53.3-66.0 kDa) was higher compared to that of alkali-soluble ones (24.9-32.6 kDa). The presence of minimal acetyl substitution (3.85-4.49 %) on xylan was unequivocally confirmed. NMR spectroscopic analysis indicated that the hemicelluloses in GSP predominantly consist of a 1,4-β-ᴅ-Xyl backbone with arabinose substituents at O-3 and 4-O-methyl-α-ᴅ-GlcA substituents at O-2 of the xylose residues. p-Coumaric acid substitution also occurred on the 1,4-β-ᴅ-Xyl backbone. Hydrothermal treatment significantly reduced the hemicelluloses' relative molar mass and produced 7-10 % xylo-oligosaccharides. Furthermore, the moderately degraded hemicelluloses exhibited significantly enhanced biological activity. Finally, the incorporation of the moderately degraded hemicelluloses imparted the galactomannan film with exceptional antioxidant properties (81.1 % DPPH scavenging activity), while negligibly affecting its transparency. Our study's findings will contribute to a comprehensive understanding of the structural and biochemical properties of hemicellulose in waste G. sinensis pods, thereby facilitating their enhanced utilization in industrial applications.